Plan to put your seedlings into the garden about 2 weeks after the date of your last spring frost. Your soil should be dug up thoroughly to get it loose for the big seedlings, and mix in some aged manure or compost while you are at it. Squash likes nutrients in its soil. Your squash spot needs full sun, and you should allow for 3 feet between each hill (you will just be planting one pot in each location, with 3 or four seedlings in it).
If you are not starting with indoor-grown seedlings, you will still have to wait for 2 weeks past the frost date. If you’ve had cool weather, you can lay black plastic down over the garden before planting to help warm up the soil. The seeds won’t sprout in the cold. Plant them in hills, just like you did with the transplants, about 3 per hill.
Many squashes can be grown vertically to save space, but this isn’t the best idea with a spaghetti squash. The fruits are just too big and it is awkward to try and support them on the vine when hanging in mid-air. It can be done, as long as you are willing to put in a bit of extra effort with your trellis and support structures.